o-ring size selection?

[hobbs101]

Hi. I have a port on a pressure vessel (14 bar). The port is 2" diameter hole. A flange plate bolts over the port. The fasteners are on a 5" PCD. I need an o-ring to seal the port. Should I select an o-ring size that is close to the port size, i.e. just over 2". Or, should I select an o-ring that is close to the fastener PCD, i.e. just less than 5"?

With the former I will be minimise the surface area that is under pressure. With the latter I'll be ensuring good clamping on the o-ring.

Thanks.

 

[hobbs101]

Any thoughts on this one anyone?

 

[btrueblood]

I've always gone with the minimum area approach, and size the bolt circle appropriately. A hand calc stress analysis, or FEA, will help predict if the flange is too soft and allow a gap to open for the o-ring to extrude through.

 

[dgallup]

The smaller the seal ID the better. Less pressure load therefore everything else can be down sized, less expensive. I like to keep cross section up when possible. Small cross sections make it much harder to control the squeeze.

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